Lubricating oil composition

ABSTRACT

A lubricating oil composition for a metal belt-type continuously variable transmission with a high metal-to-metal friction coefficient and excellent anti-fatigue and anti-seizure properties is provided. The composition contains a lubricating base oil and (A) a high overbased alkaline earth metal sulfonate having a base number of 300 to 500 mgKOH/g in an amount of 0.01 to 0.03 percent by mass as alkaline earth metal, (B) a low overbased alkaline earth metal sulfonate with a base number of 0 to 40 mgKOH/g in an amount of 0.005 to 0.015 percent by mass as alkaline earth metal, and (C) a sulfur-containing phosphite ester in an amount of 0.02 to 0.06 percent by mass as phosphorus. The ratio ([M]/[P]) of the content of (B) as alkaline earth metal ([M]) to the content of (C) as phosphorus ([P]) is 0.15 or greater.

TECHNICAL FIELD

The present invention relates to lubricating oil compositions, inparticular to a lubricating oil composition for a metal belt typecontinuously variable transmission.

BACKGROUND ART

Recent automatic transmissions or continuously variable transmissionshave been demanded to be light and small and sought to be improved inpower transmission capability in connection with the increased poweroutput of the engines with which the transmissions are used incombination. The reduction in weight and size is intended to improve thefuel efficiency of the vehicles in which the transmissions are mounted.

In the case of a metal belt type continuously variable transmission inparticular, it can be reduced in size if the friction coefficientbetween the belt and pulleys is enhanced and thus lubricating oil to beused therein is preferably an oil having properties to keep themetal-to-metal friction coefficient at a high level.

Furthermore, a lubricating oil has also been demanded to reduce the fuelconsumption of a vehicle in which the composition is used. Specifically,a lubricating oil contributes to an improvement in fuel economy byreducing its viscosity to reduce stir resistance or reduce viscousresistance upon idling of a wet clutch pack or upon fluid filmlubrication, resulting in a reduction in power loss.

A transmission fluid has been proposed, in which a friction modifier, ametallic detergent, an ashless dispersant, and an anti-wear agent areoptimally added so as to retain the friction characteristics of alock-up clutch in a good condition, provide long-lasting anti-shudderproperties or preventing the generation of scratch noise by making theμ-V characteristics between the belt and pulleys (change in frictioncoefficient against change in slipping velocity) exhibit positivegradient (see Patent Literatures 1 to 9 below).

For example, Patent Literature 1 discloses a transmission lubricatingoil composition comprising a specific calcium salicylate, an SP-basedextreme pressure additive, a specific succinimide and a boron-containingashless dispersant, each in a specific amount, which compositionexhibits excellent properties such as excellent anti-shudder propertiesand long-lasting fatigue life. Patent Literature 2 discloses acontinuously variable transmission lubricating oil compositioncontaining an organic acid metal salt with a specific composition, ananti-wear agent, and a boron-containing succinimide, as essentialcomponents, to have both higher metal-to-metal friction coefficient andanti-shudder properties for a slip control mechanism. Patent Literature3 discloses a long-lasting continuously variable transmissionlubricating oil composition comprising calcium salicylate, a phosphorousanti-wear agent, a friction modifier, and a dispersant type viscosityindex improver, to have both a higher metal-to metal frictioncoefficient and anti-shudder properties for a slip control mechanism.Patent Literature 4 discloses a lubricating oil composition comprising adithiocarbamate compound, a condensate of a branched fatty acid having 8to 30 carbon atoms and amine, and an amine-based antioxidant, to haveexcellent and long-lasting anti-shudder properties. Patent Literature 5discloses an automatic transmission fluid composition comprising calciumsulfonate, phosphorous acid esters and further a sarcosine derivative ora reaction product of a carboxylic acid and amine, to have long-lastinganti-shudder properties for a slip lock-up mechanism and long-lastingproperties to prevent scratch noise in a belt type continuously variabletransmission. Patent Literature 6 discloses an automatic transmissionfluid composition comprising a specific alkaline earth metal sulfonatein a specific amount, which composition is excellent in oxidationstability as a fluid used for an automatic transmission with a slipcontrol mechanism and has long-lasting anti-shudder properties. PatentLiterature 7 discloses an automatic transmission fluid comprisingcalcium salicylate, magnesium salicylate, a specific amount of afriction modifier and a specific amount of a boric acid-modifiedsuccinimide, with excellent anti-shudder properties and a certain torquecapacity. Patent Literature 8 discloses a continuously variabletransmission oil with excellent anti-wear properties and a high torquecapacity, comprising an overbased calcium sulfonate and orthophosphateseach in a specific amount. Patent Literature 9 discloses a lubricatingoil composition with a high metal-to-metal friction coefficient on ametal belt and long-lasting anti-shudder properties, comprising one ormore types of alkaline earth metal sulfonates or phenates containingboth a low base number alkaline earth metal salt and a high base numberalkaline earth metal salt, an imide compound, and a phosphorus compoundin specific amounts.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Laid-Open PublicationNo. 2003-113391

Patent Literature 2: Japanese Patent Application Laid-Open PublicationNo. 2001-323292

Patent Literature 3: Japanese Patent Application Laid-Open PublicationNo. 2000-355695

Patent Literature 4: Japanese Patent Application Laid-Open PublicationNo. 11-50077

Patent Literature 5: Japanese Patent Application Laid-Open PublicationNo. 10-306292

Patent Literature 6: Japanese Patent Application Laid-Open PublicationNo. 10-25487

Patent Literature 7: Japanese Patent Application Publication No.2000-63869

Patent Literature 8: Japanese Patent Application Laid-Open PublicationNo. 2008-222904

Patent Literature 9: Japanese Patent Application Laid-Open PublicationNo. 2001-288488

SUMMARY OF INVENTION Technical Problem

However, when a reduction in the viscosity of a lubricating oil isfacilitated, oil film at lubricating sites becomes thinner and thusanti-fatigue properties are deteriorated and also seizure likely occursparticularly when the oil is high in metal-to-metal frictioncoefficient. Therefore, the present invention has an object to provide alubricating oil composition which is excellent in anti-fatigueproperties and anti-seizure properties even if being reduced inviscosity while keeping the torque capacity by maintaining themetal-to-metal friction coefficient higher, particularly suitable as ametal belt type continuously variable transmission fluid.

Solution to Problem

As the results of extensive studies to achieve the above object carriedout by the inventors, the present invention has been accomplished on thebasis of the finding that the above object was able to be achieved witha lubricating oil composition comprising alkaline earth metal sulfonateseach having a specific base number and a phosphorous additive having aspecific structure each in a specific amount.

That is, the present invention provides a lubricating oil compositionfor a metal belt-type continuously variable transmission comprising alubricating base oil and (A) an high overbased alkaline earth metalsulfonate having a base number determined by a perchloric acid method of300 to 500 mgKOH/g in an amount of 0.01 to 0.03 percent by mass asalkaline earth metal, (B) a low overbased alkaline earth metal sulfonatewith a base number determined by a perchloric acid method of 0 to 40mgKOH/g in an amount of 0.005 to 0.015 percent by mass as alkaline earthmetal, and (C) a sulfur-containing phosphite ester represented bystructural formula (I) below in an amount of 0.02 to 0.06 percent bymass as phosphorus so that the ratio ([M]/[2]) of the content asalkaline earth metal ([M]) of (B) the low overbased alkaline earth metalsulfonate to the content as phosphorus ([P]) of (C) thesulfur-containing phosphite ester is 0.15 or greater:

wherein R is a sulfur-containing hydrocarbyl group having 4 to 20 carbonatoms, R¹ is hydrogen, a hydrocarbyl group having 4 to 20 carbon atomsor a sulfur-containing hydrocarbyl group having 4 to 20 carbo atoms.

The present invention also relates to the foregoing continuouslyvariable transmission lubricating oil composition further comprising (D)a phosphite ester and/or an orthophosphate ester in such an amount thatthe amount of phosphorous in the lubricating oil composition is therange of up to 0.08 percent by mass or less.

The present invention also relates to the foregoing continuouslyvariable transmission lubricating oil composition further comprising atleast one type selected from the group consisting of friction modifiers,metallic detergents, viscosity index improvers, pour point depressants,anti-oxidants, corrosion inhibitors, and anti-foamers.

Advantageous Effect of Invention

The lubricating oil composition of the present invention is alubricating oil composition that can maintain the metal-to-metalfriction coefficient at a high level, is excellent in anti-fatigueproperties, and enhanced in anti-seizure properties, particularlysuitable as a metal belt type continuously variable transmission oil.

The lubricating oil composition of the present invention is alsoexcellent in performances required for transmission fluids other thanthose described above and thus is suitably used for the automatic ormanual transmission and the differential gears, of automobiles,construction machines and agricultural machines. Moreover, thelubricating oil composition can be used as gear oils for industrialuses; lubricating oils for the gasoline engines, diesel engines or gasengines of automobiles such as two- and four-wheeled vehicles, powergenerators, and ships; turbine oils; and compressor oils.

DESCRIPTION OF EMBODIMENTS

The present invention will be described in detail below.

No particular limitation is imposed on the lubricating base oil of thelubricating oil composition of the present invention, which may,therefore, be any of mineral base oils and synthetic base oils that areused in ordinary lubricating oils.

Specific examples of the mineral base oil include those which can beproduced by subjecting a lubricating oil fraction produced byvacuum-distilling an atmospheric distillation bottom oil resulting fromatmospheric distillation of a crude oil, to any one or more treatmentsselected from solvent deasphalting, solvent extraction, hydrocracking,hydroisomerization, solvent dewaxing, and hydrorefining; wax-isomerizedmineral oils; and those produced by isomerizing GTL WAX (Gas to LiquidWax).

The mineral based oil used in the present invention is preferably ahydrocracked mineral base oil. Alternatively, the mineral base oil ispreferably a wax-isomerized isoparaffin base oil, which is produced byisomerizing a raw material oil containing 50 percent by mass or more ofwax such as a petroleum-based wax or Fischer-Tropsch synthetic oil.Although these base oils may be used alone or in combination, a sole useof a wax-isomerized base oil is preferable. Although these base oils maybe used alone or in combination, a sole use of a wax-isomerized base oilis preferable.

Specific examples of the synthetic base oils include polybutenes andhydrogenated compounds thereof; poly-α-olefins such as 1-octeneoligomer, 1-decene oligomer and 1-dodecene oligomer or hydrogenatedcompounds thereof; diesters such as ditridecyl glutarate,di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate anddi-2-ethylhexyl sebacate; polyol esters such as neopentylglycol ester,trimethylolpropane caprylate, trimethylolpropane pelargonate,pentaerythritol 2-ethylhexanoate and pentaerythritol pelargonate;aromatic synthetic oils such as alkylnaphthalenes, alkylbenzenes, andaromatic esters; and mixtures of the foregoing.

The lubricating base oil used in the present invention may be any one ofthe above-described mineral base oils and synthetic base oils or amixture of two or more types selected therefrom. For example, the baseoil may be one or more types of the mineral base oils, one or more typesof the synthetic base oils or a mixed oil of one or more types of themineral base oils and one or more types of the synthetic base oils.

Although no particular limitation is imposed on the kinematic viscosityof the lubricating base oil used in the present invention, the base oilis preferably adjusted to have a 100° C. kinematic viscosity ofpreferably 2 to 8 mm²/s, more preferably 2 to 6 mm²/s, particularlypreferably 2 to 4.5 mm²/s. A base oil with a 100° C. kinematic viscosityof greater than 8 mm²/s is not preferable because the resultinglubricating oil composition would be poor in low temperature viscositycharacteristics while a base oil with a 100° C. kinematic viscosity oflower than 2 mm²/s is not also preferable because the resultinglubricating oil composition would be poor in lubricity due to itsinsufficient oil film formation at lubricating sites and large inevaporation loss of the lubricating base oil.

No particular limitation is imposed on the viscosity index of thelubricating base oil, which is, however, preferably 100 or greater, morepreferably 120 or greater, more preferably 130 or greater, particularlypreferably 140 or greater and usually 200 or less, preferably 160 orless. The use of a lubricating base oil having a viscosity index ofgreater than 100 renders it possible to produce a composition exhibitingexcellent viscosity characteristics from low temperatures to hightemperatures. Whilst, if the viscosity index is too high, the resultingcomposition tends to be high in viscosity at low temperatures.

In order to improve the low temperature viscosity characteristics andviscosity index of the lubricating oil composition, the base oil ispreferably a combination of two or more base oils having a viscosityindex of 115 or greater selected from low viscosity base oils having aviscosity index of 115 or greater and a 100° C. kinematic viscosity of 2mm²/s or higher and lower than 3.5 mm²/s and relatively high viscositybase oils having a viscosity index of 125 or greater and a 100° C.kinematic viscosity of 3.5 mm²/s or higher and 4.5 mm²/s or lower. Inparticular, mixing these base oils can enhance the viscosity index sothat the −40° C. Brookfield viscosity is 10000 mPa·s or lower.

The viscosity index of the above-described low viscosity base oil ispreferably 120 or greater, more preferably 125 or greater and theviscosity index of the relatively high viscosity base oil is preferably130 or greater, more preferably 135 or greater so that the −40° C.Brookfield viscosity can be 8000 mPa·s or lower.

No particular limitation is imposed on the sulfur content of thelubricating base oil used in the present invention, which is, however,preferably 0.1 percent by mass or less, more preferably 0.05 percent bymass or less, more preferably 0.01 percent by mass or less, particularlypreferably 0.005 percent by mass or less, most preferably substantially0. A composition with excellent oxidation stability can be produced byreducing the sulfur content of the lubricating base oil.

No particular limitation is imposed on the evaporation loss of thelubricating base oil. However, the NOACK evaporation loss is preferablyfrom 10 to 50 percent by mass, more preferably from 20 to 40 percent bymass, particularly preferably from 22 to 35 percent by mass. The use ofa lubricating base oil with a NOACK evaporation loss adjusted within theabove ranges renders it possible to achieve both low temperaturecharacteristics and anti-wear properties. The term “NOACK evaporationloss” used herein denotes an evaporation loss measured in accordancewith CEC L-40-T-87.

The lubricating oil composition of the present invention comprises ahigh overbased alkaline earth metal sulfonate with a base numberdetermined by a perchloric acid method of 300 to 500 mgKOH/g asComponent (A).

Specific examples of the high overbased alkaline earth metal sulfonatethat is Component (A) in the present invention include: a basic saltproduced by at first producing a neutral salt (normal salt) by reactingan alkyl aromatic sulfonic acid produced by sulfonating an alkylaromatic compound having a molecular weight of 100 to 1,500, preferably200 to 700 directly with an alkaline earth metal base such as ahydroxide or oxide of an alkaline earth metal such as magnesium and/orcalcium or produced by once converting the alkyl aromatic sulfonic acidto an alkali metal salt such as a sodium salt or a potassium salt andthen substituting the alkali metal salt with an alkaline earth metalsalt and then heating the neutral salt together with an excess amount ofan alkaline earth metal salt or an alkaline earth metal base (alkalineearth metal hydroxide or oxide) in the presence of water; and overbasedsalts (ultrabasic salts) produced by reacting these neutral salts(normal salt) with a base of an alkaline earth metal in the presence ofcarbonic acid gas and/or a boron compound such as boric acid or aborate. These reactions are generally carried out in a solvent(aliphatic hydrocarbon solvents such as hexane, aromatic hydrocarbonsolvents such as xylene, and light lubricating base oil).

Specific examples of the alkyl aromatic sulfonic acids referred hereininclude petroleum sulfonic acids and synthetic sulfonic acids. Thepetroleum sulfonic acids may be those produced by sulfonating an alkylaromatic compound contained in the lubricant fraction of a mineral oilor may be mahogany acid by-produced upon production of white oil. Thesynthetic sulfonic acids may be those produced by sulfonating an alkylbenzene having a straight-chain or branched alkyl group, produced as aby-product from a plant for producing an alkyl benzene used as the rawmaterial of a detergent or produced by alkylating polyolefin to benzene,or those produced by sulfonating dinonylnaphthalene. No particularlimitation is imposed on the sulfonating agents used for sulfonatingthese alkyl aromatic compounds, which may be generally fuming sulfuricacids or sulfuric acid.

Although alkaline earth metal sulfonates as described above are usuallycommercially available as diluted with a light lubricating base oil, itis preferable to use a metallic detergent whose metal content is from1.0 to 20 percent by mass, preferably from 2.0 to 16 percent by mass.

In the present invention, Component (A) is blended in an amount of 0.01to 0.03 percent by mass, preferably 0.02 to 0.03 percent by mass asalkaline earth metal with the objective of improving metal-to-metalfriction coefficient and in view of anti-seizure properties. IfComponent (A) is blended in an amount of less than 0.01 percent by mass,the resulting composition is degraded in oxidation stability. IfComponent (A) is blended in an amount of more than 0.03 percent by mass,the resulting composition is degraded in anti-seizure properties.

The lubricating oil composition of the present invention comprises a lowoverbased alkaline earth metal sulfonate having a base number determinedby a perchloric acid method of 0 to 40 mgKOH/g as Component (B).

In the present invention, Component (B) is blended in an amount of 0.005to 0.015 percent by mass, preferably 0.005 to 0.010 percent by mass asalkaline earth metal with the objective of improving metal-to-metalfriction coefficient and in view of anti-fatigue properties andanti-seizure properties. If Component (B) is blended in an amount ofless than 0.005 percent by mass, the resulting composition is degradedin anti-fatigue properties. If Component (B) is blended in an amount ofmore than 0.015 percent by mass, the resulting composition is degradedin anti-seizure properties.

Alkaline earth metals of Component (A) and Component (B) are preferablycalcium and magnesium, particularly preferably calcium.

The lubricating oil composition of the present invention comprises asulfur-containing phosphite ester represented by structural formula (I)as Component (C).

The sulfur-containing phosphite ester that is Component (C) in thepresent invention is a mono- or di-hydrocarbyl phosphite represented bystructural formula (I) below:

In formula (I), R is a sulfur-containing hydrocarbyl group having 4 to20 carbon atoms, R¹ is hydrogen, a hydrocarbyl group having 4 to 20carbon atoms or a sulfur-containing hydrocarbyl group having 4 to 20carbon atoms.

Examples of the sulfur-containing hydrocarbyl group include hydrocarbylgroups containing a thioether bond (—CH₂—S—CH₂—) in their main chain orbranched chain.

Examples of the hydrocarbyl group include alkyl, cycloalkyl, alkenyl,cycloalkenyl, aryl, alkylaryl, and arylalkyl groups. The hydrocarbylgroup may contain halogen or a substituent such as hydroxy, nitro,cyano, and alkoxy groups.

The hydrocarbyl group is preferably an alkyl, cycloalkyl or aryl grouphaving 4 to 20, preferably 6 to 18, most preferably 8 to 16 carbonatoms. Specific examples include butyl, pentyl, hexyl, heptyl, octyl,nonyl, decyl, octadecyl, cyclohexyl and phenyl groups.

The sulfur-containing hydrocarbyl group having 4 to 20 carbon atoms ispreferably a hydrocarbyl group which is the above-described hydrocarbylgroup having 4 to 20 carbon atoms containing a thioether bond(—CH₂—S—CH₂—) in its main chain or branched chain, for example a grouprepresented by formula (II):

—(CH₂)_(m)—S—(CH₂)_(n)—CH₃  (II)

wherein m is an integer of 1 to 18, preferably 2 to 12, more preferably2 to 6, n is an integer of 2 to 18, preferably 4 to 16, more preferably6 to 14, and m+n is an integer of 3 to 19, preferably 5 to 17, morepreferably 7 to 15.

Specific examples of the sulfur-containing hydrocarbyl group having 4 to20 carbon atoms include —(CH₂)₂—S—(CH₂)₆—CH₃, —(CH₂)₂—S—(CH₂)₇—CH₃,—(CH₂)₂—S—(CH2)₈—CH₃, —(CH₂)₂—S—(CH₂)₉—CH₃, —(CH₂)₂—S—(CH₂)₁₀—CH₃,—(CH₂)₂—S—(CH₂)₁₁—CH₃, —(CH₂)₂—S—(CH₂)₁₂—CH₃, —(CH₂)₃—S—(CH₂)₆—CH₃,—(CH₂)₃—S—(CH₂)₇—CH₃, —(CH₂)₃—S—(CH₂)₈—CH3, —(CH₂)₃—S—(CH₂)₉—CH₃,—(CH₂)₃—S—(CH₂)₁₀—CH₃, —(CH₂)₃—S—(CH₂)₁₁—CH₃, —(CH₂)₃—S—(CH₂)₁₂—CH₃,—(CH₂)₄—S—(CH₂)₆—CH₃, —(CH₂)₄—S—(CH₂)₇—CH₃, —(CH₂)₄—S—(CH₂)₈—CH₃,—(CH₂)₄—S—(CH₂)₉—CH₃, —(CH₂)₄—S—(CH₂)₁₀—CH₃, —(CH₂)₄—S—(CH₂)₁₁—CH₃, and—(CH₂)₄—S—(CH₂)₁₂—CH₃.

Among these groups, particularly preferred are —(CH₂)₂—S—(CH₂)₈—CH₃(3-thiaundecyl) and —(CH₂)₂—S—(CH₂)₁₂—CH₃ (3-thiapentadecyl).

In the present invention, Component (C) is blended in an amount of 0.02to 0.06 percent by mass, preferably 0.03 to 0.05 percent by mass asphosphorous with the objective of improving metal-to-metal frictioncoefficient and in view of anti-fatigue properties and anti-seizureproperties. If Component (C) is blended in an amount of less than 0.02percent by mass, the resulting composition is degraded in anti-fatigueproperties. If component (C) is blended in an amount of more than 0.06percent by mass, the resulting composition is decreased inmetal-to-metal friction coefficient.

In the lubricating oil composition of the present invention, the ratio([M]/[P]) of the content ([M]) as metal of (B) the above-described lowoverbased alkaline earth metal sulfonate to the content ([P]) asphosphorous of (C) the above-described sulfur-containing phosphite esteris necessarily 0.15 or greater, preferably 0.20 or greater, morepreferably 0.25 or greater, particularly preferably 0.30 or greater. If[M]/[P] is less than 0.15, belt-pulley μ-V characteristics are degraded,resulting in poor scratch noise preventing properties. Whilst, the upperlimit of [M]/[P] is 0.75, preferably 0.70 or less, more preferably 0.65or less, more preferably 0.60 or less.

The lubricating oil composition of the present invention comprisespreferably a phosphite ester and/or an orthophosphate ester as Component(D).

No particular limitation is imposed on the phosphite ester and/ororthophosphate ester, but examples thereof include phosphate monoesters,phosphate diesters, phosphate triesters, phosphite monoesters, phosphitediesters, and phosphite triesters, all having a hydrocarbon group of 1to 30 carbon atoms. Alternatively, salts of these esters and amines oralkanol amines or metal salts such as zinc salt of these esters may alsobe used.

Specific examples of the orthophosphate ester include triphenylphosphate, tricresyl phosphate, trixylenyl phosphate, cresyl diphenylphosphate, xylenyl diphenyl phosphate, tris(isopropylphenyl)phosphate,tris(t-butylphenyl)phosphate, tributyl phosphate, tripentyl phosphate,trihexyl phosphate, triheptyl phosphate, trioctyl phosphate, trinonylphosphate, tridecyl phosphate, triundecyl phosphate, tridodecylphosphate, tritridecyl phosphate, tritetradecyl phosphate, tripentadecylphosphate, trihexadecyl phosphate, triheptadecyl phosphate, trioctadecylphosphate, and trioleyl phosphate.

Specific examples of the phosphite ester include monoalkyl phosphiteesters such as monopropyl phosphite, monobutyl phosphite, monopentylphosphite, monohexyl phosphite, monoheptyl phosphite, and monooctylphosphite, of which the alkyl groups may be straight-chain or branched;mono(alkyl)aryl phosphite esters such as monophenyl phosphite andmonocresyl phosphite; dialkyl phosphites such as dipropyl phosphite,dibutyl phosphite, dipentyl phosphite, dihexyl phosphite, diheptylphosphite, and dioctyl phosphite, of which the alkyl groups may bestraight-chain or branched; di(alkyl)aryl phosphite esters such asdiphenyl phosphite and dicresyl phosphite; trialkyl phosphite esterssuch as tripropyl phosphite, tributyl phosphite, tripentyl phosphite,trihexyl phosphite, triheptyl phosphite, and trioctyl phosphite, ofwhich the alkyl groups may be straight-chain or branched; tri(alkyl)arylphosphite esters such as triphenyl phosphite and tricresyl phosphite;and mixtures thereof.

In the present invention, Component (D) is blended in such an amountthat the amount of phosphorus in the composition is in the range of upto 0.08 percent by mass or less, preferably up to 0.06 percent by massor less with the objective of improving metal-to-metal frictioncoefficient and in view of anti-fatigue properties and anti-seizureproperties. If the phosphorus amount is more than 0.08 percent by mass,the resulting composition is degraded in anti-fatigue properties.

The lubricating oil composition of the present invention may be blendedwith one or more types of friction modifiers and/or metallic detergents.Blending of these additives in the lubricating oil composition of thepresent invention renders it possible to produce a lubricating oilcomposition which is more excellent for a belt type continuouslyvariable transmission equipped with a wet friction clutch.

The friction modifier that can be used in combination with thelubricating oil composition of the present invention may be any compoundthat is usually used as a friction modifier for lubricating oil.Examples of such a compound include amine compounds, fatty acid amidesand fatty acid metal salts, each having an alkyl or alkenyl group having6 to 30 carbon atoms (particularly at least one straight-chain alkyl oralkenyl group having 6 to 30 carbon atoms in their molecules).

The above-exemplified amine compounds include succinimides that arereaction products with polyamines. These include those modified with aboric compound or a phosphorus compound.

Examples of the amine compound include straight-chain or branched,preferably straight-chain aliphatic monoamines and aliphatic polyamines,each having 6 to 30 carbon atoms, alkyleneoxide adducts of thesealiphatic amines, salts of these amine compounds and phosphate esters orphosphite esters, and boric acid-modified products of(phosphite)phosphate ester salts of these amine compounds.

Particularly preferred are alkyleneoxide adducts of amine compounds;salts of these amine compounds and phosphate esters (for example,di-2-ethylhexylphosphate), phosphite esters (for example,di-2-ethylhexylphosphate); boric acid-modified products of(phosphite)phosphate ester salts of these amine compounds; and mixturesthereof.

Examples of the fatty acid amide include amides of straight-chain orbranched, preferably straight-chain fatty acids having 7 to 31 carbonatoms and aliphatic monoaminse or aliphatic polyamines. Specificexamples include lauric acid amide, lauric acid diethanol amide, lauricacid monopropanol amide, myristic acid amide, myristic acid diethanolamide, myristic acid monopropanol amide, palmitic acid amide, palmiticacid diethanol amide, palmitic acid monopropanol amide, stearic acidamide, stearic acid diethanol amide, stearic acid monopropanol amide,oleic acid amide, oleic acid diethanol amide, oleic acid monopropanolamide, coconut oil fatty acid amide, coconut oil fatty acid diethanolamide, coconut oil fatty acid monopropanol amide, synthetic mixed fattyacid amide having 12 or 13 carbon atoms, synthetic mixed fatty aciddiethanol amide having 12 or 13 carbon atoms, synthetic mixed fatty acidmonopropanol amide having 12 or 13 carbon atoms, and mixtures thereof.

Examples of the fatty acid metal salt include alkaline earth metal salts(magnesium salt, calcium salt) and zinc salts of straight-chain orbranched, preferably straight-chain fatty acids having 7 to 31 carbonatoms. More specifically, particularly preferred are calcium laurate,calcium myristate, calcium palmitate, calcium stearate, calcium oleate,coconut oil fatty acid calcium, synthetic mixed fatty acid calciumhaving 12 or 13 carbon atoms, zinc laurate, zinc myristate, zincpalmitate, zinc stearate, zinc oleate, coconut oil fatty zinc, syntheticmixed fatty zinc having 12 or 13 carbon atoms, and mixtures thereof.

In the present invention, any one or more types of compounds selectedfrom these friction modifiers may be blended in any amount but thecontent thereof is usually preferably from 0.01 to 5 percent by mass,more preferably from 0.03 to 3 percent by mass on the basis of the totalmass of the lubricating oil composition.

Examples of the metallic detergent that can be used in combination withthe lubricating oil composition of the present invention include alkalimetal sulfonates, alkaline earth metal sulfonates other than Component(A) and Component (B), alkali metal phenates or alkaline earth metalphenates, and alkali metal salicylates or alkaline earth metalsalicylates. Among these metallic detergents, alkaline earth metaldetergents are preferably used.

When the metallic detergents is blended in the present invention, it isblended in an amount of preferably 0.01 percent by mass or more, morepreferably 0.1 percent by mass or more, more preferably 0.15 percent bymass or more on the basis of the total mass of the composition in viewof rust prevention. It is also blended in an amount of preferably 2percent by mass or less, more preferably 1.5 percent by mass or less,more preferably 1 percent by mass or less, most preferably 0.8 percentby mass or less on the basis of the total mass of the composition inview of thermal stability and life of anti-oxidation properties.

In order to further enhance the properties of the lubricating oilcomposition of the present invention, it may be blended with any one ormore of conventional lubricating oil additives, such as ashlessdispersants, viscosity index improvers, anti-oxidants, corrosioninhibitors, anti-foamers and colorants.

The ashless dispersants that can be used in combination with thelubricating oil composition of the present invention may be anycompounds that are used as ashless dispersants for lubricating oil.Examples of such compounds include nitrogen-containing compounds havingper molecules at least one alkyl or alkenyl group having 40 to 400,preferably 60 to 350 carbon atoms, bis-type or mono-type succinimideshaving an alkenyl group having 40 to 400 carbon atoms, preferably 60 to350 carbon atoms, and modified products produced by allowing thesecompounds to react with boric acid, phosphoric acid, carboxylic acid orderivatives thereof, or a sulfur compound. Any one or more of thesecompounds may be used in combination.

The alkyl or alkenyl group referred herein may be straight-chain orbranched but is preferably a branched alkyl or alkenyl group derivedfrom oligomers of olefins such as propylene, 1-butene or isobutylene ora cooligomer of ethylene and propylene. The alkyl or alkenyl group ispreferably polybutenyl group derived from polymers produced bypolymerizing a butene mixture or a high purity isobutylene with analuminum chloride-based catalyst or a boron fluoride-based catalyst,particularly preferably those from which a halogen compound is removed.

If the carbon number of the alkyl or alkenyl group is fewer than 40, theashless dispersant would be poor in detergent dispersibility. Whilst, ifthe carbon number of the alkyl or alkenyl group exceeds 400, theresulting lubricating oil composition would be degraded in lowtemperature fluidity. Although the content of these compounds arearbitrarily selected, it is preferably from 0.1 to 10 percent by mass,more preferably 1 to 8 percent by mass on the basis of the total mass ofthe lubricating oil composition. The ashless dispersants that may beused in combination in the present invention are particularly preferablysuccinimides having a polybutenyl group and a weight-average molecularweight of 700 to 3,500, preferably 900 to 2,000 and/or boricacid-modified compounds thereof with the objective of further improvingshifting properties. With the objective of enhancing the ability toavoid the peel-off of a wet clutch, the ashless dispersants are blendedwith preferably a boric acid-modified succinimide, more preferably aboric acid-modified succinimide as one type of component.

Specific examples of viscosity index improvers that can be used incombination with the lubricating oil composition of the presentinvention include non-dispersant type viscosity index improvers such ascopolymers of one or more monomers selected from various methacrylateesters or hydrogenated compounds thereof; and dispersant type viscosityindex improvers such as copolymers of various methacrylate estersfurther containing nitrogen compounds. Specific examples of otherviscosity index improvers include non-dispersant- or dispersant-typeethylene-α-olefin copolymers of which α-olefin may be propylene,1-butene, or 1-pentene, or a hydrogenated compound thereof;polyisobutylenes or hydrogenated compounds thereof; styrene-dienehydrogenated copolymers; styrene-maleic anhydride ester copolymers; andpolyalkylstyrenes.

The molecular weight of these viscosity index improvers is necessarilyselected, taking account of the shear stability thereof. Specifically,the number-average molecular weight of the non-dispersant or dispersanttype polymethacrylate is from 5,000 to 150,000, preferably from 5,000 to35,000. The number-average molecular weight of polyisobutylenes orhydrogenated compounds thereof is from 800 to 5,000, preferably from1,000 to 4,000. The number-average molecular weight of ethylene-α-olefincopolymers or hydrogenated compounds thereof is from 800 to 15,000,preferably from 3,000 to 12,000. Among these viscosity index improvers,the use of ethylene-α-olefin copolymers or hydrogenated compoundsthereof renders it possible to produce a lubricating oil compositionwhich is particularly excellent in shear stability. One or morecompounds selected from these viscosity index improvers may be blendedin any amount in the lubricating oil composition of the presentinvention. However, the content of the viscosity index improver isusually from 0.1 to 40 percent by mass, on the basis of the total massof the composition.

The anti-oxidant may be any anti-oxidant that has been usually used inlubricating oil, such as phenol- or amine-based compounds. Specificexamples of the anti-oxidant include alkylphenols such as2-6-di-tert-butyl-4-methylphenol; bisphenols such asmethylene-4,4-bisphenol(2,6-di-tert-butyl-4-methylphenol);naphthylamines such as phenyl-α-naphthylamine; dialkyldiphenylamines;zinc dialkyldithiophosphoric acids such asdi-2-ethylhexyldithiophosphoric acid; and esters of(3,5-di-tert-butyl-4-hydroxyphenyl)fatty acid (propionic acid) with amonohydric or polyhydric alcohol such as methanol, octadecanol,1,6-hexanediol, neopentyl glycol, thiodiethylene glycol, triethyleneglycol and pentaerythritol. Any one or more compounds selected fromthese compounds may be contained in any amount, which is, however,usually from 0.01 to 5.0 percent by mass on the basis of the total massof the composition.

The corrosion inhibitors that can be used in combination with thelubricating oil composition of the present invention may be anycompounds that have been usually used as corrosion inhibitors forlubricating oil. Examples of such compounds include triazole-typecompounds such as benzotriazole and tolyltriazole, thiadiazole-, andimidazole-types compounds. Anyone or more of compounds selected fromthese compounds may be contained in any amount, which is, however,usually from 0.01 to 3.0 percent by mass on the basis of the total massof the composition.

The anti-foamer that can be used in combination with the lubricating oilcomposition of the present invention may be any compounds that have beenusually used as anti-foaming agents for lubricating oil. Examples ofsuch compounds include silicones such as dimethylsilicone andfluorosilicone. Any one or more of compounds selected from thesecompounds may be contained in any amount, which is, however, usuallyfrom 0.001 to 0.05 percent by mass on the basis of the total mass of thecomposition.

The colorants that may be used in combination with the transmissionlubricating oil composition of the present invention may be anycolorants and contained in any amount, which is, however, desirouslyfrom 0.001 to 1.0 percent by mass on the basis of the total mass of thelubricating oil composition.

EXAMPLES

Hereinafter, the present invention will be described in more detail byway of the following examples and comparative examples, which should notbe construed as limiting the scope of the invention.

Examples 1 to 10 and Comparative Examples 1 to 11

Lubricating oil compositions of the examples and comparative examplesset forth in Table 1 were prepared and subjected to the following tests,the results of which are also set forth in Table 1. Each additive inTable 1 is added in an amount on the basis of the total mass of thecomposition.

(1) Last non-seizure load (LNSL) evaluated by Four-Ball Extreme PressureTest Method in accordance with ASTM D2783

(2) Wear scar diameter evaluated by Four-Ball Extreme Pressure TestMethod in accordance with ASTM D4172

(3) Seizure load evaluated by Falex Seizure test in accordance with ASTMD 3233

(4) Metal-to-metal friction coefficient evaluated by LFW-1 Test inaccordance with JASO Method M358:2005

TABLE 1 Examples 1 2 3 4 5 6 7 8 Mineral oil 1) mass % Balance BalanceBalance Balance Balance Balance Balance Balance High overbased Casulfonate 2) ppm/Ca 250 250 250 100 250 250 250 High overbased Casulfonate 3) ppm/Ca 250 Low overbased Ca sulfonate 4) ppm/Ca Lowoverbased Ca sulfonate 5) ppm/Ca 100 100 100 100 100 100 100 60 Highoverbased Ca salicylate 6) ppm/Ca High overbased Ca phenate 7) ppm/CaTotal ppm/Ca 350 350 350 350 200 350 350 310 Sulfur-containing ppm/P 300300 300 300 300 600 200 300 phosphite ester 8) Phosphite ester 9) ppm/P300 Phosphate ester 10) ppm/P 300 Acid phosphate ester 11) ppm/P Totalppm/P 300 300 600 600 300 600 200 300 Other performance additives 12)mass % 13.0 13.0 13.0 13.0 13.0 13.0 13.0 13.0 [M]/[P] — 0.33 0.33 0.330.33 0.33 0.17 0.50 0.20 (Low basic Ca/sulfur-containing P) Fatigue life(L50) 13) h 110 105 105 110 105 120 80 95 Metal-to-metal friction —0.131 0.132 0.137 0.138 0.130 0.132 0.132 0.13 coefficient 14) SeizureLoad 15) N 1050 1050 1050 1050 1050 1150 1000 1050 ISOT remaining basemgKOH/g 0.5 0.5 0.5 0.5 0.3 0.5 0.5 0.5 number 16) Metal-to-metalfriction 0.93 0.92 0.93 0.93 0.92 0.98 0.89 0.98 characteristics (uVcharacterisitcs) 17) Examples Comparative Examples 9 10 1 2 3 4 5Mineral oil 1) mass % Balance Balance Balance Balance Balance BalanceBalance High overbased Ca sulfonate 2) ppm/Ca 250 250 250 250 250 250High overbased Ca sulfonate 3) ppm/Ca Low overbased Ca sulfonate 4)ppm/Ca 100 Low overbased Ca sulfonate 5) ppm/Ca 150 50 100 100 100 Highoverbased Ca salicylate 6) ppm/Ca High overbased Ca phenate 7) ppm/CaTotal ppm/Ca 400 300 350 350 250 100 350 Sulfur-containing ppm/P 600 200800 300 300 300 phosphite ester 8) Phosphite ester 9) ppm/P Phosphateester 10) ppm/P 600 Acid phosphate ester 11) ppm/P Total ppm/P 600 200800 600 300 300 300 Other performance additives 12) mass % 13.0 13.013.0 13.0 13.0 13.0 13.0 [M]/[P] — 0.25 0.25 0.13 — 0.00 0.33 0.00 (Lowbasic Ca/sulfur-containing P) Fatigue life (L50) 13) h 120 80 140 55 70110 85 Metal-to-metal friction — 0.131 0.13 0.119 0.132 0.130 0.1320.131 coefficient 14) Seizure Load 15) N 1150 1000 1150 1000 1050 10501050 ISOT remaining base mgKOH/g 0.4 0.5 0.5 0.5 0.5 0 0.5 number 16)Metal-to-metal friction 0.95 0.93 1.08 0.85 1.15 0.93 1.12characteristics (uV characterisitcs) 17) Comparative Examples 6 7 8 9 1011 Mineral oil 1) mass % Balance Balance Balance Balance Balance BalanceHigh overbased Ca sulfonate 2) ppm/Ca 250 500 250 250 High overbased Casulfonate 3) ppm/Ca Low overbased Ca sulfonate 4) ppm/Ca Low overbasedCa sulfonate 5) ppm/Ca 250 100 100 100 60 150 High overbased Casalicylate 6) ppm/Ca 250 High overbased Ca phenate 7) ppm/Ca 250 Totalppm/Ca 500 350 350 600 310 400 Sulfur-containing ppm/P 300 300 300 300550 800 phosphite ester 8) Phosphite ester 9) ppm/P Phosphate ester 10)ppm/P 300 Acid phosphate ester 11) ppm/P Total ppm/P 300 300 300 600 550800 Other performance additives 12) mass % 13.0 13.0 13.0 13.0 13.0 13.0[M]/[P] — 0.83 0.33 0.33 0.33 0.11 0.19 (Low basic Ca/sulfur-containingP) Fatigue life (L50) 13) h 110 70 65 105 110 140 Metal-to-metalfriction — 0.130 0.131 0.132 0.137 0.13 0.117 coefficient 14) SeizureLoad 15) N 750 1050 1050 750 1100 1200 ISOT remaining base mgKOH/g 0.40.9 0.4 0.7 0.5 0.4 number 16) Metal-to-metal friction 0.85 0.93 0.920.93 1.10 0.98 characteristics (uV characterisitcs) 17) The footnotes ofTable 1 are as follows: 1) 100° C. kinematic viscosity: 3.0 mm²/s,viscosity index 109, S content 0.1 percent by mass or less 2) basenumber 300 mgKOH/g, Ca content 11.6 percent by mass 3) base number 500mgKOH/g, Ca content 18.0 percent by mass 4) base number 80 mgKOH/g, Cacontent 4.5 percent by mass 5) base number 20 mgKOH/g, Ca content 2.4percent by mass 6) base number 170 mgKOH/g, Ca content 6.3 percent bymass 7) base number 250 mgKOH/g, Ca content 9.3 percent by mass 8)3-thiopentylhydrogen phosphite 9) dibutylhydrogen phosphite 10)tricresyl phosphate 11) butyl acid phosphate 12) ashless dispersant,anti-oxidant, viscosity index improver, friction modifier, sealingagent, metal deactivators 13) Four-ball fatigue life test (IP 300):rotation speed 3000 rpm, temperature 120° C., contact pressure 3.9 GPa14) Block on ring test (LFW-1): load 400N, sliding velocity 0.05 m/s,temperature 80° C. 15) Pin/V-block seizure test: rotation speed 290 rpm,temperature 80° C. 16) Base number determined by a hydrochloric acidmethod at 165.5° C., after 72 hours 17) Block on ring test (LFW-1): load90N, slipping velocity 0 to 0.2 m/s, temperature 60° C. When the ratio(μ2/μ20) of the friction coefficient at a slipping velocity of 0.2 m/sto that at a slipping velocity of 0.02 m/s is 1 or less, in particularless than 1, the μ-V slope is a positive gradient and thus thecomposition is evaluated as being excellent in scratch noise preventingproperties.

As apparent from the results set forth in Table 1, Comparative Example 4wherein (A) the high overbased alkaline earth metal sulfonate is blendedin an amount of less than 0.01 percent by mass as calcium is lower inISOT remaining base number than the examples and likely to be poor inoxidation stability while Comparative Example 9 wherein the same isblended in an amount of more than 0.03 percent by mass is lower inseizure load than the examples and likely to be poor in anti-seizureproperties. Comparative Examples 7 and 8 containing an high overbasedalkaline earth metal salicylate and an high overbased alkaline earthmetal phenate, respectively are shorter in anti-fatigue life than theexamples and thus likely to be poor in anti-fatigue properties.

Comparative Examples 3 and 5 wherein (B) the low overbased alkalineearth metal sulfonate is blended in an amount of less than 0.005 percentby mass as calcium are shorter in anti-fatigue life than the examplesand likely to be poor in anti-fatigue properties while ComparativeExample 6 wherein the same is blended in an amount of more than 0.015percent by mass is lower in seizure load than the examples and likely tobe poor in anti-seizure properties.

Comparative Example 2 wherein (C) the sulfur-containing phosphite esteris blended in an amount of less than 0.02 percent by mass as phosphorousis shorter in anti-fatigue life than the examples and likely to be poorin anti-fatigue properties while Comparative Examples 1 and 11 whereinthe same is blended in an amount of more than 0.06 percent by mass arelower in metal-to-metal friction coefficient than the examples and givean adverse effect on torque capacity.

Comparative Example 10 wherein the content ([P]) of (B) the lowoverbased alkaline earth metal sulfonate as phosphorous and the content([M]) of (C) the sulfur-containing phosphite ester as metal are withinthe ranges as defined by the present invention but the ratio ([M]/[P])is less than 0.15 is negative in μ-V gradient evaluated by the block onring test when compared with the examples and likely to be poor inbelt-pulley scratch noise preventing properties.

1. A lubricating oil composition for a metal belt-type continuouslyvariable transmission comprising a lubricating base oil and (A) an highoverbased alkaline earth metal sulfonate having a base number determinedby a perchloric acid method of 300 to 500 mgKOH/g in an amount of 0.01to 0.03 percent by mass as alkaline earth metal, (B) a low overbasedalkaline earth metal sulfonate with a base number determined by aperchloric acid method of 0 to 40 mgKOH/g in an amount of 0.005 to 0.015percent by mass as alkaline earth metal, and (C) a sulfur-containingphosphite ester represented by structural formula (I) below in an amountof 0.02 to 0.06 percent by mass as phosphorus so that the ratio([M]/[P]) of the content as alkaline earth metal ([M]) of (B) the lowoverbased alkaline earth metal sulfonate to the content as phosphorus([P]) of (C) the sulfur-containing phosphite ester is 0.15 or greater:

wherein R is a sulfur-containing hydrocarbyl group having 4 to 20 carbonatoms, R¹ is hydrogen, a hydrocarbyl group having 4 to 20 carbon atomsor a sulfur-containing hydrocarbyl group having 4 to 20 carbo atoms. 2.The lubricating oil composition for a metal belt-type continuouslyvariable transmission according to claim 1 further comprising (D) aphosphite ester and/or an orthophosphate ester in such an amount thatthe amount of phosphorous in the lubricating oil composition is therange of up to 0.08 percent by mass or less.
 3. The lubricating oilcomposition for a metal belt-type continuously variable transmissionaccording to claim 1 further comprising at least one type selected fromthe group consisting of friction modifiers, metallic detergents,viscosity index improvers, pour point depressants, anti-oxidants,corrosion inhibitors, and anti-foamers.
 4. The lubricating oilcomposition for a metal belt-type continuously variable transmissionaccording to claim 2 further comprising at least one type selected fromthe group consisting of friction modifiers, metallic detergents,viscosity index improvers, pour point depressants, anti-oxidants,corrosion inhibitors, and anti-foamers.